Chemical, mechanical and morphological properties of hypomineralized enamel of permanent first molars

Abstract Objective. The microstructure of hypomineralized enamel in permanent teeth has been described in several studies as less distinct prism sheaths and disorganized enamel with lack of organization of the enamel crystals. The mechanical properties, hardness and modulus of elasticity of the hypomineralized enamel have lower values compared with normal. The aim of this study was to examine normal and hypomineralized enamel using scanning electron microscopy (SEM), hardness measurements and X-ray microanalysis (XRMA). Material and methods. Four extracted hypomineralized permanent first molars, sectioned and cut in half, were analyzed with SEM, XRMA and hardness measurements. Results. An inverse relation was found between the micro hardness and the Ca:C ratio in hypomineralized and normal enamel. The acid-etched hypomineralized enamel appeared on SEM to be covered with a structureless layer and the prisms appeared disorganized, with thick prism sheaths and loosely packed crystallites. Furthermore, bacteria were found deep in porous hypomineralized enamel close to the enamel-dentin junction. Conclusions. Teeth diagnosed with molar incisor hypomineralization have significantly lower hardness values in the hypomineralized enamel compared with normal enamel. The hardness values vary according to the morphological and chemical properties.